A fuel cell system for obtaining electric energy by an electrochemical reaction between a hydrogen gas and an oxidation gas is known. The hydrogen gas serving as a fuel for this fuel cell system is flammable and odorless. On the other hand, in handling a hydrogen gas, it is preferable to be able to recognize the presence of the hydrogen gas with certainty.
Therefore, a hydrogen supply apparatus that mixes a hydrogen gas with an odorant whose presence is recognizable due to its odor has been provided (see, for example, Patent Document 1). In this hydrogen supply apparatus, since the hydrogen gas and the odorant are mixed, the handling of the hydrogen gas is facilitated. Further, in the case where the leakage of the hydrogen gas has occurred, for example, the leakage of the hydrogen gas can be immediately detected due to the odor of the odorant.    [Patent document 1] JP 2002-29701 A    [Patent document 2] JP 2002-216812 A    [Patent document 3] JP 2004-111167 A